A group of fourteen qualifying Users have detailed a broad range of experimental plans that require flow cytometry analysis as summarized herein: 1) Analysis of lymphoid cell populations for the presence or absence of constitutive and/or inducible cell surface marker expression in response to xenobiotic-induced and/or accelerated systemic autoimmunity; 2) Use of autoantibodies to study gene specific cell cycle regulation, tissue expression of transgenic autoantigen, and autoantigen fate during apoptosis; 3) Analysis of the role of mitochondria and intracellular acidification during cell death; 4) Expression and fate of transcription factors in hematopoiesis and leukemia, using selection and sorting of retroviral infected cells with specific cDNAs and GFP; 5) Analysis of autoepitopes in autoimmune thrombocytopenia and effect of autoantibodies on megakaryocytopoiesis; 6) Studies on lymphohematopoietic cells and their activation status in response to hepatitis B, and C virus infection in humans, chimpanzee and mice; 7) Studies on structure and expression of platelet membrane receptors and their role in platelet function; 8) Analysis of repair of mitochondrial dysfunction through gene transfection, and analysis of repair via measurement of membrane potential, reactive oxygen species and cell growth; 9) Characterization of signaling pathways in airway inflammation, using selection and sorting of transfected airway epithelial cells; 10) Development of new detection: - methods to identify mutations associated with chronic granulomatosus disease; 11) Analysis of adhesive and metastatic properties of tumor cell variants using selection and sorting to isolate stable transfectants expressing mutant forms of integrins; 12) Analysis of the assembly, transport and expression of the high affinity IgE receptor, complex using cells transfected with various components of the complex; 13) and 14) Studies in transplantation which examine the delivery of potential therapeutic genes to target cell populations via infection with retroviral vectors. Flow cytometry will be used to select and sort cell populations prior to and after transplantation studies.